The increased demand for lithium batteries has resulted in research to improve the cycle life and calendar life of these batteries. Conventional lithium ion batteries typically use non-aqueous electrolytes with a lithium salt such as LiPF6 dissolved in carboxylic ester solvents such as ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, etc. The electrolytes are then placed in an electrochemical cell using lithium transition metal oxides as the cathode and carbon or graphite as the anode. Such conventional electrolyte solvents are very flammable and volatile, and can be oxidatively cleaved into gaseous products above 4.4V vs Li/Li+. A variety of electrolytes that include silicon-based solvents such as, polysiloxanes and silanes, have been developed to address these issues. However, many secondary batteries that include these solvents exhibit poor capacity and/or cycling performance. There remains a need for a battery that has the safety provided by polysiloxane solvents, but which exhibits acceptable capacity and/or cycling capability.
It is generally accepted that electrolyte composition is one of the decisive factors affecting the efficient and long-term operation of Li-ion batteries, as well as their safety for users. The chemical nature of the electrolyte components affects not only lithium ion transport through the electrolyte, but also the structure and composition of a passive layer (often called the solid electrolyte interphase, or SEI) which forms on the carbon anode upon charging. The industry standard electrolyte is ethylene carbonate (EC), which exhibits excellent SEI forming properties, despite its poor, low-temperature performance. Other potential solvents, while having favorable transport properties, may not necessarily provide satisfactory passivation of graphite. For example, propylene carbonate (PC), has been shown to co-intercalate with lithium cations into the crystal structure of graphite, followed by decomposition of the PC. A number of electrolyte additives have developed to address the co-intercalation problem associated, to enable the use of PC-based electrolytes. Other available solvents, such as silanes may be reduced on the surface of the graphite anode and not compatible with graphite anode for the formation of its own SEI. In order to solve the above problems, the use of additives is one effective solution to improve lifetime, capacity, and low temperature performance of a battery. Nevertheless, common additives such as vinylene carbonates, sulfites, sulfates, and phosphates tend to be costly, and only provide for marginal electrolyte improvement.